Blue light has outstanding transmission characteristics in the sea, and is known to cause the most sensitive visual response in common squid Todarodes pacificus. Application of a light emitting diode (LED) that can efficiently emit monochromatic light is expected to bring enormous energy savings. LED can produce cost-effective low-wattage irradiance at the specific wavelength. This study investigated the retinular responses of common squid T pacificus to colored LED lights and light adaptation conditions based on the Perkinje effect, which is the tendency for the luminance sensitivity of the human eye to shift depending on the bright and dark adaptation states. The changes of the retinular response to blue, red and white LED were investigated in the bright and dark adaptation conditions in the water tank experiment. The degree of light adaptation was similar between the bright adaptation state and dark adaptation state to blue light, which suggests that squid retina is highly sensitive to blue light as it has been reported to date. On the other hand, the degree of light adaptation to red LED light showed a tendency to increase, albeit slightly, over time. However, the degree of light adaptation to white light with wide wavelength band showed similar tendencies as to the case of red light in the dark adaptation condition, and was actually superior to the case of blue light in the bright adaptation condition. Also, the degree of light adaptation of the retina cells collected from the sea experiment was found to be between the range of 20 and 40%. From these results, blue light may be regarded as an excellent luring source as the retina of squid is highly sensitive to it, but it cannot be determined as the most ideal LED color for the purpose of catching fish. (C) 2012 Elsevier Ltd. All rights reserved.